Assessment of GenoType MTBDRplus assay performance compared to culture using respiratory and non-respiratory samples in Scotland

Abstract number: P2046

Objectives: The GenoType MTBDRplus (MTBDR+) assay (HAIN Lifescience) was evaluated for rapid, direct detection of Mycobacterium tuberculosis complex (MTBC) and simultaneous resistance to rifampicin (RIF) and isoniazid (INH) in specimens using line-probe technology. The MTBC detection and drug susceptibility results were compared to those obtained by culture and Bactec MGIT 960.

Methods: 322 specimens (266 respiratory and 56 non-respiratory) that were AFB-positive (n = 293) or had high suspicion of TB were examined from June 2006 to November 2009. MTBDR+ testing was performed once weekly as part of the routine reference laboratory service. Additionally 96 MTBC cultures were extracted for INH and RIF resistance testing only and the results compared to phenotypic susceptibility results.

Results: The MTBDR+ assay was positive for MTBC in 182 specimens. Compared to culture the sensitivity, specificity, positive and negative predictive values for the MTBDR+ assay were 84.9%, 85.4%, 89.6% and 79.3% respectively. 11 of 29 MTBC-culture positive specimens not detected by MTBDR+ contained large numbers of AFB on microscopy. 19 of 154 (12.3%) MTBC culture-positive respiratory specimens produced negative MTBDR+ results. 10 MTBC culture-negative respiratory specimens and 4 non-respiratory specimens that gave positive results using the MTBDR+ assay were from known TB patients. No specimens contained PCR inhibitors. Assay sensitivity for MTBC detection was 87.7% for 266 respiratory specimens and 73.7% for 56 non-respiratory samples.

163 of the 170 (95.9%) specimens with interpretable resistance results and found to contain MTBC were sensitive to both RIF and INH. INH mono-resistance was detected in 6 specimens and both RIF- and INH-resistance was detected in a single specimen. The MTBDR+ resistance results were confirmed in all 122 cases where Bactec MGIT 960 results were available. For the 96 culture extracts, 98.9% of MTBDR+ RIF and 86.7% of INH resistance results concurred with the phenotypic susceptibility results.

Conclusions: The MTBDR+ assay is appropriate for weekly batching of small specimen numbers. Assay sensitivity was 87.7% for respiratory specimens but reduced for non-respiratory specimens. 19 MTBC cases 'missed' using MTBDR+ require further investigation. Overall, the direct RIF resistance results correlated well with BACTEC MGIT 960 but some INH resistant strains may be missed.

MTBDRplus result

Culture result

MTBC

NEG

MOTT

Total

MTBC-POS

163

19

0

182

MTBC-NEG

29

39

72

140

Total

192

58

72

322

Session Details

Date:

10/04/2010

Time:

00:00-00:00

Session name:

Abstracts 20th European Congress of Clinical Microbiology and Infectious Diseases